As the Obama administration confronts the latest terrorism threat in Yemen, its diplomatic and development efforts are being constrained by a shortage of resources, a lack of in-house expertise and a fraught history with a Yemeni leader deeply ambivalent about American help. Administration officials said they focused on Yemen as a hothouse for Islamic terrorism from the day President Obama took office. The United States has tripled its foreign assistance to the country from 2008 levels and plans to spend up to $63 million on Yemen this year. But by all accounts, that is a modest amount for a country that is suddenly a central threat on the foreign policy landscape; it is roughly the same amount the United States sends to Serbia. It illustrates how much the United States is stretched on the foreign policy front, and how hard it is to extend its resources beyond the wars in Iraq and Afghanistan. Beyond providing military and intelligence help - showcased in recent airstrikes on training sites for Al Qaeda - the administration has yet to develop a coherent plan for dealing with Yemen’s pervasive poverty and corruption, according to former diplomats and outside experts. Those ills, they say, are at the root of Yemen’s lure for terrorists.